In a bi-directional communication system, an antenna receives a first communication signal over the air and transfers a second communication signal over the air. The antenna transfers the first communication signal to a base station, and the base station transmits the second communication signal to the antenna. The base station and antenna may also operate in a time-division manner, where the base station and antenna transmit during transmit time periods and receive during receive time periods. These transmit and receive time periods repeatedly alternate over time.
The transmitted and received communications signals may be comprised of multiple frequency channels where one system in the base station transmits and receives over a first frequency channel, and a second system in the base station transmits and receives over a second frequency channel. During transmit time periods, the frequency channels are combined to form the transmitted communication signal. During receive time periods, the frequency channels are separated from the received communication signal. Various devices are used to combine these frequency channels for transmission and separate these frequency channels upon reception. Resonant cavities use wave-guides to combine and separate communication signals. Unfortunately, resonant cavities are relatively large and expensive. Hybrid microwave combiners use couplers and splitters to combine and separate communication signals. Unfortunately, hybrid microwave combiners introduce unacceptable loss and are also relatively expensive.